Dual fluid cartridges are used to store and dispense two fluids which must be kept separate until the time of use and then, at the time of dispensing, need to be mixed together very quickly in a precise pre-set ratio to ensure that the proper chemical reaction takes place. If the cartridge does not dispense the two fluids properly in the required pre-set ratio, the final fluid mixture may be greatly affected and may not function or adhere as required. Examples of such fluids are those that are used to create thermoset adhesives (i.e., a resin and a hardener).
Dual fluid cartridges have been used in industry for the last twenty years and, over the years, differing types of dual fluid cartridges have been developed. FIG. 1 depicts one relatively recently developed dual fluid cartridge that has been particularly effective. Such dual fluid cartridges can be filled relatively easily and can be used in readily available dispensers, such as caulking guns as is shown in FIG. 2. An example of such a dual fluid cartridge that is presently in use is depicted in FIG. 3. Another example is described and depicted in U.S. Pat. No. 5,310,091, entitled “Dual Product Dispenser”, (“'091 patent”) which is commonly owned with this application and is incorporated by reference herein. However, with designs such as the one depicted in FIG. 3, there tends to be a significant amount of residual fluid waste left in the cartridge once the product has been completely dispensed due to the open volume between the cartridge post, such as the post 82 in FIG. 3, and the inner diameter of the cartridge delivery tube, such as the delivery tube 54 in FIG. 3, through which such post 82 moves. Such residual waste increases cost due to the fluid left in the cartridge and also has the effect of potentially raising serious environmental and disposal issues, depending on the type of fluids being discharged. Much of this waste could be reduced or eliminated if the diameter of the post was increased in relation to the inner diameter of the delivery tube or, vice versa, if the diameter of the inner delivery tube was decreased in relation to the diameter of the post, as depicted in the figures of the '091 patent. However, because the post 82 completely fills the interior of the delivery tube 54 in such an approach, this type of approach has the very undesirable effect of increasing the back pressure generated as the fluids are pushed through the cartridge. This is a very significant drawback, considering that such cartridges are typically used in hand held applications and a cartridge design that generates any significant amount of back pressure causes the cartridge to be very difficult, if not impossible, to use.
Accordingly, there is a need for a dual fluid cartridge that is effective in reducing the residual waste left in a cartridge after all the product has been dispensed, while at the same time not generating an unacceptable level of back pressure.